The use of fossil fuel in gas turbine engines results in the combustion products consisting of carbon monoxide, carbon dioxide, water vapor, particulates, unburned hydrocarbons, nitrogen oxides and sulfur oxides. Of these above products, carbon dioxide and water vapor are considered normal and unobjectionable. In most applications, governmental imposed regulations, are further restricting the remainder of the species mentioned above emitted in the exhaust gases.
In the past, the majority of the products of combustion have been controlled by design modifications. For example, at the present time particulates in the gas turbine exhaust have been controlled either by design modifications to the combustor and fuel injector or by removing them by traps and filters. Sulfur oxides are normally controlled by the selection of fuels that are low in total sulfur. This leaves carbon monoxide, unburned hydrocarbons and nitrogen oxides as the emissions of primary concern in the exhaust gases being emitted from the gas turbine engine.
Oxides of nitrogen are produced in two ways in conventional combustion systems. For example, oxides of nitrogen are formed at high temperatures within the combustion zone by the direct combination of atmospheric nitrogen and oxygen or by the presence of organic nitrogen in the fuel. The rates with which nitrogen oxides form depends mostly upon the flame temperature and, to some degree upon the concentration of the reactants. Consequently, a small reduction in flame temperature can result in a large reduction in the nitrogen oxides.
Past and some present systems provide gaseous fuel burner systems that include a burner tube and a primary burner head having a plurality of primary burner ports in a two dimensional array, over a selected, substantially planar area, transverse to the burner tube. A mixture of gaseous fuel and primary air is supplied to the burner tube, and to the primary burner ports. Secondary burner ports are provided upstream of the primary burner ports which carry the gaseous fuel and primary air in the form of jets, mixing with the secondary air, and burning to provide combustion products CO2 and H2O, which flow downstream with the secondary air into the combustion zone of the primary burner. An example of such a system is disclosed in U.S. Pat. No. 4,157,890 issued Jun. 12, 1979, to Robert D. Reed.
Another example of an injector nozzle is disclosed in U.S. Pat. No. 4,483,137 issued Nov. 20, 1984, to Robie L. Faulkner. The patent discloses an injector in which provision is made for introducing a liquid coolant into the combustor of the engine. This reduces the flame temperature in the combustor, thereby discouraging the formation of thermal NOx.
In an attempt to reduce NOx emissions, gas turbine combustion systems have utilized a variety of structurally configured injector nozzles. The above system and injector nozzles used therewith are examples of attempts to reduce the emissions of oxides of nitrogen. The nozzles described above fail to efficiently mix the gaseous fluids with the combustion air, and if using water and air, to control the emissions of oxides of nitrogen emitted from the combustor.